If it's a standard Java API, working examples of that API are irrelevant. Look for working examples of any standard Java API, e.g. Apache POI. The questions you have on integration will be answered by that. Questions on using the API should be addressed by the Intuit API documentation.
One aspect to bear in mind is that the standard Java policy in Domino restricts quite a bit, particularly Java reflection. If the Intuit Java API uses Java reflection to convert JSON to Java objects and vice versa, you will need to amend the Java policy, use AccessController.doPrivileged to elevate permissions or possibly wrap such calls and the API in an OSGi plugin. But you'll need to try and, if necessary, investigate further to verify if you need to do that.
